The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed in Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"—is a largely discredited biological hypothesis that in developing from embryo to adult (ontogeny), animals go through stages resembling or representing successive stages in the evolution of their remote ancestors (phylogeny). Since embryos also evolve in different ways, within the field of developmental biology the theory of recapitulation is seen as a historical side-note rather than as dogma.[1][2][3]

With different formulations, including the early Meckel-Serres Law, such ideas have been applied and extended to several fields and areas, including the origin of language, religion, biology, cognition and mental activities,[4] anthropology,[5] education theory[6] and developmental psychology.[7] Recapitulation theory is still considered plausible and is applied by some researchers in fields such as the study of the origin of language,[8]cognitive development,[9] and behavioral development in animal species.[10]

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The earliest recorded trace of a recapitulation theory is from the Egyptian Pharaoh Psamtik I (664 – 610 BCE), who used it as a hypothesis on the origin of language.[11][12] The concept of recapitulation was first formulated outside the field of biology. It was widely held among traditional theories of the origin of language (glottology), being assumed as a premise that children's use of language gives insights on its origin and evolution.[13]

Ernst Haeckel attempted to synthesize the ideas of Lamarckism and Goethe's Naturphilosophie with Charles Darwin's concepts. While often seen as rejecting Darwin's theory of branching evolution for a more linear Lamarckian "biogenic law" of progressive evolution, this is not accurate: Haeckel used the Lamarckian picture to describe the ontogenetic and phylogenetic history of individual species, but agreed with Darwin about the branching of all species from one, or a few, original ancestors.[19] Since early in the twentieth century, Haeckel's "biogenetic law" has been refuted on many fronts.[3]

Haeckel formulated his theory as "Ontogeny recapitulates phylogeny". The notion later became simply known as the recapitulation theory. Ontogeny is the growth (size change) and development (shape change) of an individual organism; phylogeny is the evolutionary history of a species. Haeckel claimed that the development of advanced species passes through stages represented by adult organisms of more primitive species.[3] Otherwise put, each successive stage in the development of an individual represents one of the adult forms that appeared in its evolutionary history.

For example, Haeckel proposed that the pharyngeal grooves between the pharyngeal arches in the neck of the human embryo not only roughly resembled gill slits of fish, but directly represented an adult "fishlike" developmental stage, signifying a fishlike ancestor. Embryonic pharyngeal slits, which form in many animals when the thin branchial plates separating pharyngeal pouches and pharyngeal grooves perforate, open the pharynx to the outside. Pharyngeal arches appear in all tetrapod embryos: in mammals, the first pharyngeal arch develops into the lower jaw (Meckel's cartilage), the malleus and the stapes. But these embryonic pharyngeal arches, grooves, pouches, and slits in human embryos can not at any stage carry out the same function as the gills of an adult fish.

Haeckel produced several embryo drawings that often overemphasized similarities between embryos of related species. The misinformation was propagated through many biology textbooks, and popular knowledge, even today. Modern biology rejects the literal and universal form of Haeckel's theory, such as its possible application to behavioural ontogeny, i.e. the psychomotor development of young animals and human children.[20]

Haeckel's drawings were disputed by Wilhelm His, who had developed a rival theory of embryology.[21] His developed a "causal-mechanical theory" of human embryonic development.[22]

Darwin's view was that embryos resembled each other, since they shared a common ancestor, which presumably had a similar embryo, but that development did not necessarily recapitulate phylogeny: in his view, there was no reason to suppose that an embryo at any stage resembled an adult of any ancestor. Darwin supposed further that embryos were subject to less intense selection pressure than adults, and had therefore changed less.[23] Modern evolutionary developmental biology (evo-devo), on the other hand, points to active evolution of embryonic development as a significant means of changing the morphology of adult bodies. Two of the key principles of evo-devo, namely that changes in the timing (heterochrony) and positioning within the body (heterotopy) of aspects of embryonic development would change the shape of a descendant's body compared to an ancestors, were however first formulated by Haeckel in the 1870s. These elements of his thinking about development have thus survived, whereas his theory of recapitulation has not.[24]

The Haeckelian form of recapitulation theory is considered defunct.[25] However, embryos do undergo a period where their morphology is strongly shaped by their phylogenetic position, rather than selective pressures.[26]

"Embryos do reflect the course of evolution, but that course is far more intricate and quirky than Haeckel claimed. Different parts of the same embryo can even evolve in different directions. As a result, the Biogenetic Law was abandoned, and its fall freed scientists to appreciate the full range of embryonic changes that evolution can produce—an appreciation that has yielded spectacular results in recent years as scientists have discovered some of the specific genes that control development."[27]

Although Haeckel's specific form of recapitulation theory is now discredited among biologists, the strong influence it had on social and educational theories of the late 19th century still resonates in the 21st century. Research in the late 20th century confirmed that "both biological evolution and the stages in the child’s cognitive development follow much the same progression of evolutionary stages as that suggested in the archaeological record."[9]

English philosopher Herbert Spencer was one of the most energetic promoters of evolutionary ideas to explain many phenomena. He compactly expressed the basis for a cultural recapitulation theory of education in the following claim, published in 1861, five years before Haeckel first published on the subject:[6]G. Stanley Hall used Haeckel's theories as the basis for his theories of child development.

If there be an order in which the human race has mastered its various kinds of knowledge, there will arise in every child an aptitude to acquire these kinds of knowledge in the same order.... Education is a repetition of civilization in little.[28]

— Herbert Spencer

Developmental psychologist Jean Piaget favored a weaker version of the formula, according to which ontogeny parallels phylogeny because the two are subject to similar external constraints.[29]

The Austrian pioneer in psychoanalysis, Sigmund Freud, also favored Haeckel's doctrine. He was trained as a biologist under the influence of recapitulation theory at the time of its domination, and retained a Lamarckian outlook with justification from the recapitulation theory.[30] He also distinguished between physical and mental recapitulation, in which the differences would become an essential argument for his theory of neuroses.[30]

More recently, several art historians, most prominently musicologist Richard Taruskin, have applied the term "ontogeny becomes phylogeny" to the process of creating and recasting art history, often to assert a perspective or argument. For example, the peculiar development of the works by modernist composer Arnold Schoenberg (here an "ontogeny") is generalized in many histories into a "phylogeny" – a historical development ("evolution") of Western music toward atonal styles of which Schoenberg is a representative. Such historiographies of the "collapse of traditional tonality" are faulted by art historians as asserting a rhetorical rather than historical point about tonality's "collapse".[31]

Taruskin also developed a variation of the motto into the pun "ontogeny recapitulates ontology" to refute the concept of "absolute music" advancing the socio-artistic theories of Carl Dalhaus. Ontology is the investigation of what exactly something is, and Taruskin asserts that an art object becomes that which society and succeeding generations made of it. For example, composer Johann Sebastian Bach's St. John Passion, composed in the 1720s, was appropriated by the Nazi regime in the 1930s for propaganda. Taruskin claims the historical development of the Passion (its ontogeny) as a work with an anti-Semitic message does, in fact, inform the work's identity (its ontology), even though that was an unlikely concern of the composer. Music or even an abstract visual artwork can not be truly autonomous ("absolute") because it is defined by its historical and social reception.[31]

^Blechschmidt, Erich (1977) The Beginnings of Human Life. Springer-Verlag Inc., pg. 32: "The so-called basic law of biogenetics is wrong. No buts or ifs can mitigate this fact. It is not even a tiny bit correct or correct in a different form, making it valid in a certain percentage. It is totally wrong."

^Ehrlich, Paul; Richard Holm; Dennis Parnell (1963) The Process of Evolution. New York: McGraw–Hill, pg. 66: "Its shortcomings have been almost universally pointed out by modern authors, but the idea still has a prominent place in biological mythology. The resemblance of early vertebrate embryos is readily explained without resort to mysterious forces compelling each individual to reclimb its phylogenetic tree."

Faulty logic and problematic proposals relating the development of an individual to the development of the species turn up even today. The hypothesis that ontogeny recapitulates phylogeny has been applied and extended in a number of areas, including cognition and mental activities.

"...the premise that was inherent in it — that language ontogenesis reenacts language phylogenesis in a chronologically condensed way — is, arguably, a plausible one. Traditional glottogenetic theories have been implicitly shaped by it; and several current scientific approaches have adopted it as a working principle. Vico made it a basic tool of his reconstructive method."

While ontogeny does not generally recapitulate phylogeny in any direct sense (Gould 1977), both biological evolution and the stages in the child’s cognitive development follow much the same progression of evolutionary stages as that suggested in the archaeological record (Borchert and Zihlman 1990, Bates 1979, Wynn 1979) ... Thus, one child, having been shown the moon, applied the word ‘moon’ to a variety of objects with similar shapes as well as to the moon itself (Bowerman 1980). This spatial globality of reference is consistent with the archaeological appearance of graphic abstraction before graphic realism.

^Polskie Towarzystwo Socjologiczne (1986) The Polish sociological bulletin: Números 57–72 p.40 quotation: Haeckel's law is currently applied to the development of language and Psammetichus' experiment is mentioned in the handbook of history of linguistics as "something like as a first application [of Haeckel's" law] in the science of language."

^Richards, Robert J. 2008. The Tragic Sense of Life: Ernst Haeckel and the Struggle Over Evolutionary Thought. Chicago: University of Chicago Press. Pp. 136–142

^Gerhard Medicus (1992). "The Inapplicability of the Biogenetic Rule to Behavioral Development"(PDF). Human Development. 35 (1): 1–8. doi:10.1159/000277108. ISSN0018-716X. Retrieved 2008-04-30. The present interdisciplinary article offers cogent reasons why the biogenetic rule has no relevance for behavioral ontogeny. ... In contrast to anatomical ontogeny, in the case of behavioral ontogeny there are no empirical indications of 'behavioral interphenes, that developed phylogenetically from (primordial) behavioral metaphenes. ... These facts lead to the conclusion that attempts to establish a psychological theory on the basis of the biogenetic rule will not be fruitful.

^"Making visible embryos: Forgery charges". University of Cambridge. Retrieved 2016-10-27. Rütimeyer’s ex-colleague, Wilhelm His, who had developed a rival, physiological embryology, which looked, not to the evolutionary past, but to bending and folding forces in the present. He now repeated and amplified the charges, and lay enemies used them to discredit the most prominent Darwinist. But Haeckel argued that his figures were schematics, not intended to be exact. They stayed in his books and were widely copied, but still attract controversy today.

^"Wilhelm His, Sr". Embryo Project Encyclopedia. 2007. Retrieved 2016-10-27. In 1874 His published his Über die Bildung des Lachsembryos, an interpretation of vertebrate embryonic development. After this publication His arrived at another interpretation of the development of embryos: the concrescence theory, which claimed that at the beginning of development only the simple form of the head lies in the embryonic disk and that the axial portions of the body emerge only later.